Combined ac-dc to dc converter

ABSTRACT

The invention relates to a combined AC-DC to DC converter. The converter ( 100, 300, 700, 740, 780, 800, 840, 880 ) provides the option of coupling to an AC supply source ( 103, 303, 703, 803 ) with at least one phase and the further option of coupling to at least one DC supply source ( 101, 102, 301, 701, 702, 801 ). The converter ( 100, 300, 700, 740, 780, 800, 840, 880 ) obtains supply from at least one supply source at a time; and the converter ( 100, 300, 700, 740, 780, 800, 840, 880 ) contains controllable contact means that are, upon switching between supply sources, capable of connecting and disconnecting the individual supply sources to/from the converter ( 100, 300, 700, 740, 780, 800, 840, 880 ), whereby a pulse signal is generated. The converter ( 100, 300, 700, 740, 780, 800, 840, 880 ) contains at least one coil ( 112, 113, 312 ) that is in connection with at least one DC output ( 125, 126, 325, 725, 726, 825 ). The proposed converter ( 100, 300, 700, 740, 780, 800, 840, 880 ) distinguishes itself over the prior art in that switching between supply sources is accomplished by means of the contact means over a period of time, where the pulse signal is divided into periods; and wherein the periods alternatingly originate from at least one first supply source and at least one second supply source; and wherein the current pulses from the first supply source is regulated in dependence on the current pulses from the second supply source; and wherein the converter contains means for voltage regulating at least one DC output ( 125, 126, 325, 725, 726, 825 ). Hereby a flexible converter ( 100, 300, 700, 740, 780, 800, 840, 880 ) is obtained that can obtain supply from an AC supply source and one or more DC supply sources ( 101, 102, 103, 303, 701, 702, 703, 801, 803 ); and wherein switching between a first supply source and a second supply source can be accomplished without supply failures; and wherein, in overload situations, it is possible to draw on two or more supply sources.

[0001] The invention relates to a combined AC-DC to DC-converter, in thefollowing designated a converter. The converter provides at least one DCoutput from at least one AC supply with at least one phase and at leastone DC supply. The AC supply supplying an AC signal comprising positiveand negative half-periods. The converter comprises at least one coilthat is in connection with said at least one DC output. The convertercontains controllable contact means adapted for connecting anddisconnecting said AC supply and said DC supply to/from said converter

[0002] Patent application No. WO 0033451 teaches a converter unit forconverting two or more DC voltage levels from the input of the converterunit to a DC voltage on the output of the converter unit, wherein theconverter unit comprises controllable switch means that are able toconnect and disconnect the individual DC input voltage level for formingan oscillating signal, and wherein the converter unit comprisesfiltering means for lowpass filtering of the oscillating signal forforming the DC voltage on the output of the converter unit.

[0003] However, the converter unit is presents the inconvenience that itcannot connect to an AC supply source. Additionally, the converter unitis not capable of performing a gradual switch of supply source withoutsupply loss, see the below description of a method. Nor is the converterunit capable of performing an adaptive switch in case of overloadsituations.

[0004] U.S. Pat. No. 5,751,564 discloses a switch power supply systemthat is able to connect two or more different power sources withdifferent voltage levels and that are able to support power withoutpower failure, even in case the primary power source is low orcompletely absent. The output voltage is more constant than is the caseof a conventional switch power supply, and the internal loss is alsosmaller. As a result of this, the back-up supply time is more protractedthan that of a conventional UPS system. Finally, when taken into use ineg a notebook computer, there is no need to use an AC to DC adapter whenconnection is made to an AC power supply, it being possible to connectthe switch power supply directly to the AC power supply.

[0005] However, the circuit is not capable of performing anuninterrupted switching between an AC supply source and a DC supplysource.

[0006] It is the object of the invention to provide a converter that canobtain supply from one or more supply sources that can be an AC sourcewith one or more phases in combination with one or more DC sources,wherein switching form a first supply source to a second supply sourceis accomplished gradually without supply failure; and wherein—inoverload situations—it is possible to rely on one or more supplysources.

[0007] This can be accomplished in that the switching between supplysources is accomplished by connecting and disconnecting the supplysources to/from said converter based on phase information of the ACsignal, whereby the supply signal fed to said coil is divided intoperiods, wherein the periods of the supply signal alternatinglyoriginate from either positive or negative half-periods of the AC signaland current pulses from said DC supply; and wherein the current pulsesfrom the DC supply are regulated in dependence of the AC signal; andwherein the converter contains means for voltage regulating said atleast one DC output.

[0008] Hereby a flexible converter is achieved that can obtain supplyfrom an AC supply source and one or more DC supply sources; and whereinswitching from a first supply source to a second supply source can beaccomplished without supply loss; and wherein—in overload situations—twoor more supply sources can be relied on. In a typical overload situationwith an AC source in the form of a current network from a dieselgenerator and a DC source in the form of a battery, the advantage ofthis converter is that the current from the AC source can be maintainedon a constant highest value in that supplementary energy is suppliedfrom the DC source. Hereby it is possible to use smaller cables andfuses in the AC source without such fuses being blown upon overload.

[0009] The term ‘supply source’ is used herein to designate either an ACsource with one or more phases connected via a common point ofreference, or a DC source or two DC sources that are connected in seriesvia a common point of reference, whereby a positive and a negativesupply voltage are obtained.

[0010] The converter is characterised in that the AC supply source is asingle-phase AC source and that at least one DC source is provided.

[0011] Hereby a converter for single-phase systems is obtained thatprotects against supply failures in case of abrupt switching between thesingle-phase AC supply source and one, optionally more, DC sources.

[0012] The converter is characterised in that the AC supply source is apolyphase AC source and that at least one DC source is provided.

[0013] Hereby a converter for polyphase systems is obtained thatprotects against supply failures in case of abrupt switching between thepolyphase AC supply source and one, optionally more, DC sources.

[0014] The converter is characterised in that, on the basis of a signalfrom a current detector that measures the current through a coil, acontrol circuit has means for connecting and disconnecting,respectively, the one terminal of the coil to/from a DC supply source;and means to connect and disconnect, respectively, the second terminalof the coil to/from a common point of reference. The current through thecoil flows to the DC output of the converter during periods when thesecond terminal of the coil is not connected to the common point ofreference. The converter is provided with means for connecting anddisconnecting, respectively, an AC supply source to the one terminal ofthe coil, ie that terminal on the coil that can also be connected to theDC source.

[0015] Hereby a converter is obtained that has the smallest possiblenumber of components and that is simultaneously capable of performing agradual switch between supply sources; wherein the one supply source isan AC supply source; and the second supply source is a DC supply source.The converter protects against supply failures during abrupt switchesbetween supply sources.

[0016] The converter is characterised in that at least one converter isused to form a DC output that is positive relative to a common point ofreference; and at least one converter is used to form a DC output thatis negative relative to a common point of reference.

[0017] Hereby a converter is obtained that is able to deliver apositive, optionally more positive, DC output voltages, and onenegative, optionally more negative DC output voltages that are protectedagainst supply failures during abrupt switches between supply sources.

[0018] The converter is characterised in that the AC supply source isshared for the converters that are used for form a positive outputvoltage and the converters that are used to form a negative outputvoltage relative to a common point of reference.

[0019] Hereby a converter is obtained that makes requirements to thesmallest possible number of AC supply sources. This is a major advantagein that, thus, the converter can also be used where the availability ofAC supply sources is scarce.

[0020] The converter is characterised in that the means for connectingand disconnecting, respectively, the one terminal of the coil to/from aDC supply source is a controllable switch. The controllable switch canbe regulated to be connected for at least a part of every otherhalf-period.

[0021] Hereby it is possible to regulate the period of time when supplyis obtained from the DC supply source. This is associated with theadvantage that it enables parallel coupling of a number of converters tothe same battery. Each converter is then allocated a period of time thatis different from that of the other converters, during which theconverters obtain energy exclusively from the DC supply source. Theoption of parallel coupling converters to the same DC supply source alsomeans that supply can be obtained by using as few DC sources aspossible.

[0022] The converter is characterised in that the means for connectingand disconnecting, respectively, the second terminal of the coil to/froma common point of reference is a controllable switch. The controllableswitch can be regulated to be connected for at least a part of everyother half-period, and the controllable switch is typically connected inburst series.

[0023] Hereby it is possible to regulate the voltage through the coil.On the one hand it makes it possible to perform a gradual switching inconsumption of energy from the DC source, and on the other hand it makesit possible to adjust the nominal output voltage on the converter withina field. The option of adjusting the nominal output voltage of theconverter within a field means that the same converter design can beused where there is a requirement for several different output voltages.Hereby the number of different converters can be reduced.

[0024] The converter is characterised in that semi-conducters are usedas controllable switches comprising at least one of the types of fieldeffect transistor, bipolar transistor, Insulated Gate Bipolar Transistor(IGBT), Gate Turn-Off Tyristor (GTO) and Injection Enhanced GateTransistor (IEGT).

[0025] Hereby it is possible to select semi-conductor technology whiletaking into consideration requirements to supply, construction andspace.

[0026] The converter is characterised in that—in an overloadsituation—the current from the AC supply source is limited to a constantlargest value, in that supplementary energy is supplied from the DCsupply source.

[0027] Hereby a gentle load of the AC support source is obtained,wherein the converter does not expose the AC supply source to overload.

[0028] The invention will now be described in further detail withreference to the accompanying figures, wherein

[0029]FIG. 1 shows a single-phase combined AC-DC to DC converter withpositive as well as negative output voltage; and

[0030]FIG. 2 shows curves of a ramp-in course for a single-phasecombined AC-DC to DC converter with positive as well as negative outputvoltage; and

[0031]FIG. 3 shows a single-phase combined AC-DC to DC converter withpositive output voltage; and

[0032]FIG. 4 shows curves of a ramp-in course for a three-phase combinedAC-DC to DC converter with positive as well as negative output voltage;and

[0033]FIG. 5 shows curves of an overload course for a single-phasecombined AC-DC to DC converter with positive as well as negative outputvoltage; and

[0034]FIG. 6 shows curves of an overload course for a three-phasecombined AC-DC to DC converter with positive as well as negative outputvoltage; and

[0035]FIG. 7 shows a three-phase combined AC-DC to DC converter withpositive as well as negative output voltage constructed from threeconverters with shared DC supply; and

[0036]FIG. 8 shows a three-phase combined AC-DC to DC converter withpositive output voltage constructed from three converters with shared DCsupply.

[0037]FIG. 1 shows a single-phase combined AC-DC to DC converter 100with positive as well as negative output voltage. The positive terminalon a battery 101 is connected to the anode on a tyristor 106. Thenegative terminal on the battery 101 is connected to a common point ofreference 104. The cathode on the tyristor 106 is connected to thecathode on a diode 119. The gate on the tyristor 106 is connected to anoutput on a control circuit 108. The cathode on the tyristor 106 isconnected to a coil 112. A current sensor 114 encloses the connectionbetween the tyristor 106 and the coil 112. The current sensor 114 isconnected to an input on the control circuit 108. The coil 112 isfurther connected to collector on a transistor 110. Collector on thetransistor 110 is connected to the anode on a diode 121. Emitter on thetransistor 110 is connected to the common point of reference 104. Anoutput on the control circuit 108 is connected to the base of thetransistor 110. The cathode on the diode 121 is connected to a capacitor123 and to a DC output 125. The capacitor 123 is further connected tothe common point of reference 104. The DC output 125 is connected to thecontrol circuit 108. The negative terminal on a battery 102 is connectedto the cathode on a tyristor 107. The positive terminal on the battery102 is connected to the common point of reference 104. The anode on thetyristor 107 is connected to the anode on a diode 120. The gate on thetyristor 107 is connected to an output on a control circuit 109. Theanode on the tyristor 107 is connected to a coil 113. A current sensor115 encloses the connection between the tyristor 107 and the coil 113.The current sensor 115 is connected to an input on the control circuit109. The coil 113 is further connected to emitter on a transistor 111.Emitter on the transistor 111 is connected to the cathode on a diode122. Collector on the transistor 111 is connected to the common point ofreference 104. An output on the control circuit 109 is connected to thebase of the transistor 111. The anode on the diode 122 is connected to acapacitor 124 and to a DC output 126. The capacitor is further connectedto the common point of reference 104. The DC output 126 is connected tothe control circuit 109. The anode on the diode 119 is connected to anode 118. The cathode on the diode 120 is connected to the node 118. Thenode 118 is connected to a switch 127. The switch 127 is furtherconnected to a single-phase AC source 103 and to the input of asynchronising circuit 105. The single-phase AC source 103 is furtherconnected to the common point of reference 104. The one output of thesynchronising circuit 105 is connected to an input on the controlcircuit 108, and the second output of the synchronising circuit 105 isconnected to an input on the control circuit 109, and the third outputof the synchronising circuit 105 is connected to a control input on theswitch 127.

[0038] It is the task of the synchronising circuit 105 to register whenthe AC source 103 is present with a valid voltage with a view toconnecting the AC source 102 to the converter 100 via the switch 127.Besides, the synchronising circuit 105 serves the purpose ofsynchronising to the AC supply by generating synchronous control signalsto the control circuits 108, 109 with a known phase relative to the ACsupply. In the positive half-period of the single-phase AC source 103,the current flows from the single-phase AC-source 103 through thecontact 127, further through the diode 119, and further through the coil112. If the transistor 110 is interrupted, the current flows from thecoil 112 further through the diode 121 to the DC output 125, and if thetransistor 110 is connected, the current flows from the coil 112 to thecommon point of reference 104. The tyristor 106 is disconnected for thisperiod. In the negative half-period of the single-phase AC source 103,the control circuit 108 switches on the tyristor 106, whereby thecurrent from the battery 101 flows through the tyristor 106 and furtherthrough the coil 112. If the transistor 110 is interrupted, the currentflows from the coil 112 to the DC output 125, and if the transistor 1 10is connected, the current flows from the coil 112 to the common point ofreference 104. The control circuit 108 controls the transistor 110 withpulses of varying duty-cycle, and at a frequency that is usuallyconsiderably more elevated than the frequency of the single-phase ACsource 103. The auxiliary circuit consisting of the coil 112, thetransistor 110 and the diode 121 constitutes a boost converter. Duringperiods when the transistor 110 is connected the current increases inthe coil 112. During periods when the transistor is disconnected, thecurrent flows on through the diode 121 to the DC output 125 and willsimultaneously start to decrease, the voltage above the coil 112 nowhaving opposite polarity sign. Regulation of the duty-cycle for thetransistor 110 enables regulation of the current in the coil 112 andthus also the voltage on the DC output 125. The valid duty cycle for thetransistor 110 is determined by the control circuit 108 on the basis ofthe output voltage that is measured via a return coupling from the DCoutput 125. The capacitor 123 smoothens the voltage on the DC output 125to a DC voltage. In the negative half-period of the single-phase ACsource 103, the current flows to the single-phase AC-source 103 from theswitch 127, further from the diode 120, and further from the coil 113.If the transistor 111 is disconnected, the current flows to the coil 113further from the diode 122 from the DC output 126, and in case thetransistor 111 is connected, the current flows to the coil 113 from thecommon point of reference 104. The tyristor 107 is, for this period oftime, disconnected. In the positive half-period of the single-phase ACsource 103, the control circuit 109 switches on the tyristor 107,whereby the current to the battery 102 is caused to flow from thetyristor 107 and on from the coil 113. If the transistor 111 isdisconnected, the current flows to the coil 113, from the diode 122,from the DC output, and if the transistor 111 is connected, the currentflows to the coil 113 from the common point of reference 104. Thecontrol circuit 109 controls the transistor 111 with pulses of varyingduty-cycle and at a frequency that is usually considerably more elevatedthan the frequency of the single-phase AC source 103. The auxiliarycircuit consisting of the coil 113, the transistor 111, and the diode122 constitutes a boost converter. During periods when the transistor111 is connected, the current increases in the coil 113. In periods whenthe transistor 111 is disconnected, the current flows on from the diode122 from the DC output 126 and will simultaneously start to decrease,the voltage above the coil 113 now having opposite polarity sign.Regulation of the duty-cycle for the transistor 111 enables regulationof the current in the coil 113 and thus the voltage on the DC output126, too. The valid duty-cycle for the transistor 111 is determined bythe control circuit 109 on the basis of the output voltage that ismeasured via a return coupling from the DC output 126.

[0039] The capacitor 124 smoothens the voltage on the DC output 126 to aDC voltage. The regulation consists of two independent regulationsystems, one for the positive output voltage in the control circuit 108and another for the negative output voltage in the control circuit 109.Each of these regulation systems has the object of maintaining aconstant output voltage and simultaneously absorbing a current with apredetermined well-defined curve shape, whether the current comes fromthe AC source or the DC source. This is accomplished in practice byusing for each of the two control circuits 108 and 109 two regulatorloops, one that maintains the curve-shape on the current, and anotherwhose task it is to maintain the constant output voltage. The regulatorloop that determines the current curve shape will usually be the fastestof the two regulator loops. It emits on the output a pulse-widthmodulated signal to one of the two transistors 110 or 111. Each time thetransistor 110, 111 is switched on, the current in the coil 112, 113will increase. Each time it is switched off, the current will decrease,the voltage above the coil 112, 113 having in that case the oppositepolarity sign. In practice this current control can be performed inaccordance with various principles that either keep a constant orvariable frequency, or control in accordance with the instantaneous oraverage value of the current, averaged over several pulses. Thesevarious principles must be considered to be prior art and all are ableto control the current in the coil 112, 113 of a converter 100 to followoptimally the amplitude and the curve-shape on a supplied signal. Thisis accomplished by comparing the measured value of the current to asignal that corresponds to the desired voltage and continuously adaptingthe pulse/break-ratio. The current in the coil 112, 113 will all thetime either increase or decrease, but is regulated continuously with thepulse/break-ratio, such that—averaged over several pulses—it correspondsto the desired curve-shape. The term ‘pulses’ as used in this context isintended to designate control pulses for the transistor 110, 111 thatwill normally be an elevated frequency compared to the current networkfrequency. This regulator loop receives a signal with a curve-shape andamplitude that corresponds to the current that it is desired that therelevant converter 100 shall draw at a given time. This curve-shape issubsequently referred to as the current reference. The curve-shape ofthis of the current reference depends on the operating mode of theconverter 100. When it is desired to draw current from the AC source 103only, the curve-shaped will be positive and negative half-periods,respectively, of a sinusoidal signal, such that the total amount ofcurrent that is drawn from the net will become sinusoidal. This is thecurve-shape that is seen as curve 231 in FIG. 1 during the time 236.When it is desired to draw current from the battery 101, 102 only, thereference to both halves of the converter 100 will exclusively be DCsignals, since—in that case—it is desired to draw a constant DC currentfrom the battery 101, 102. When it is desired to draw current from bothsources, the current reference will have an appearance that correspondsto the curve 231 in FIG. 2 during the time 235. This curve-shapeconsists partly of sinusoidal half-waves and partly of rectangular ortrapezoidal pulses. The current reference described can either begenerated as a voltage or current curve-shape of an electronic circuit,or it can be a digitally computed curve-shape, generated by eg amicroprocessor or a Digital Signal Processor (DSP). In order to know inwhich of the described operation forms, the run is performed, a detectorcircuit 105 is present that decides whether the AC source 103 is presentand has an acceptable voltage quality. When this has been complied with,AC operation is selected. If the AC source 103 disappears or is in anyother way detected to be unacceptable as to either voltage or frequency,switching is performed to battery-operation. When the AC voltage isagain present and acceptable, a ramp-in course is made, line in FIG. 2.The detector circuit 105 can be shared by both converters. In order togenerate the desired curve shapes, a synchronisation unit 105 is alsoused. It also receives the AC signal and synchronizes to this AC signal.It is thereby able to emit phase information to the twocontrol/regulator units 109 and 109 that tells where in time one isrelative to the zero transit on the AC signal, eg as a degree figurebetween zero and 360 degrees. Such phase information is subsequentlyused to determine the course in time of the described curve-shapes. Inaddition to said signals concerning operating mode and synchronisation,it must also be possible to continuously adapt the amplitude on thedescribed current references. By changing the amplitude on the signals,the amount of current to be drawn from the AC source 103 or the DCsource 101, 102 is changed, and thus how much power is supplied to theconverter 100. This power supply must continuously be adapted to exactlycover the need for power that is drawn from the converter 100 output(s)plus what can be ascribed to loss. In case more power is supplied thanneeded, it would mean that the voltage on the capacitors 123 or 124 willcontinue to increase, and correspondingly the voltages will decrease iftoo little power is supplied. In order to thereby maintain the correctoutput voltage there is therefore in each of the control/regulatorcircuits 108 and 109 a regulator loop that measures the voltages on 125and 126 and compares them to suitable reference values. In case theoutput voltage deviates from the desired, the amplitudes on thedescribed current reference signals are regulated upwards or downwards.Only one specific maximum value for the current drawn from the AC source103 is allowed at all times. During a ramp-in course, this maximum valueis increased linearly from zero to a predetermined maximum value withina predetermined period, eg 10 seconds. If it is desired to supply morecurrent or power than allowed by this maximum value, there is formed, onthe one hand, half-wave shaped sinusoidal signals with the maximallyallowed value, whereas the remainder of the power need is covered bycurrent pulses from the battery. The distribution between the two pulsesis calculated continuously, such that they combine to cover the need forsupplied power. Correspondingly, this limitation of AC current pulses isused to delimit the current from a current network or diesel generatorduring overload. Also in this case it is calculated how much supplementis needed from the battery to deliver the requisite total amount ofpower. If the node 118 is split and if the AC source 103 and the switch127 are connected instead to the alternating current inputs of arectifier bridge, where the positive output of the rectifier bridge isconnected to the anode on the diode 119, and the negative output of therectifier bridge is connected to the cathode on the diode 120, it isalso possible to obtain supply from the AC source 103 in bothhalf-periods to both the positive half-and the negative half of theconverter 100. Hereby the power consumption from the batteries 101; 102can be reduced.

[0040]FIG. 2 shows curves of a ramp-in course for a single-phasecombined AC-DC to DC converter 100 with positive as well as negativeoutput voltage. A first curve 231 shows the current through the coil112. A second curve 232 shows the current through the coil 113. A thirdcurve 233 shows the total current of the single-phase AC source 103. Tothe first curve 231, and the second curve 232 and the third curve 233 itapplies that a first period of time 234 shows supply exclusively fromthe batteries 101, 102 and a second period of time 235 shows a ramp-incourse with supply from the batteries 101, 102 and the single-phase ACsource 103, where the current from the batteries 101, 102 is reduced inpace with the current from the single-phase AC current 103 beingincreased, and further a third period of time 236 that shows supplyexclusively from the single-phase AC source 103.

[0041] During the period of time 234, the batteries 101, 102 supplyalone the combined AC-DC to DC converter 100. During the period 235 aramp-in course takes place, where supply is accomplished from thebatteries 101, 102 as well as from the single-phase AC source 103. Thestrength of the pulse current from the batteries 101, 102 is reduced inpace with the pulse current from the single-phase AC source 103 beingincreased. During the period of time 236 the single-phase AC source 103delivers exclusively to the combined AC-DC to DC converter 100.

[0042]FIG. 3 shows a single-phase combined AC-DC to DC converter 300with positive output voltage. The positive terminal on a battery 301 isconnected to the anode on a tyristor 306. The negative terminal on thebattery 301 is connected to the anode on a tyristor 306. The negativeterminal on the battery 301 is connected to a common point of reference304. The cathode on the tyristor 306 is connected to the cathode on adiode 319. The gate on the tyristor 306 is connected to an output on acontrol circuit 308. The cathode on the tyristor 306 is connected to acoil 312. A current sensor 314 encloses the connection between thetyristor 306 and the coil 312. The current sensor 314 is connected to aninput on the control circuit 308. The coil 312 is further connected to acollector on a transistor 310. Collector on the transistor 310 isconnected to the anode on a diode 321. Emitter on the transistor 310 isconnected to the common point of reference 304. An output on the controlcircuit 308 is connected to the base of the transistor 310. The cathodeon the diode 321 is connected to a capacitor 323 and to a DC output 325.The capacitor 323 is further connected to the common reference point304. The DC output 325 is connected to the control circuit 308. Theanode on the diode 319 is further connected to switch 327. The switch327 is further connected to a single-phase AC source 303 and to theinput of a synchronization circuit 305. The single-phase AC source 303is further connected to the common reference point 304. The one outputof the synchronisation circuit 305 is connected to an input on thecontrol circuit 308, and the second output of the synchronisationcircuit 305 is connected to a control input on the switch 327.

[0043] The indication of functionality for a single-phase combined AC-DCto DC converter 300 with positive output voltage, in accordance withFIG. 3, follows the indication of functionality for the positive half ofa single-phase combined AC-DC to DC converter 100 with positive as wellas negative output voltage, in accordance with FIG. 1. Like thesingle-phase combined AC-DC to DC converter 100 with positive as well asnegative output voltage, the AC source 303 and the switch 327 caninstead be coupled to the alternating-current inputs of a rectifierbridge, where the positive output of the rectifier bridge is connectedto the anode on the diode 319, and the negative output of the rectifierbridge is connected to the reference point 304. Hereby it is possible toobtain supply from the AC source 303 in both half-periods to theconverter 300. Hereby the power consumption from the battery 301 can bereduced.

[0044]FIG. 4 shows curves of a ramp-in course for a three-phase combinedAC-DC to DC converter 700, 740, 780 with positive as well as negativeoutput voltage. A first curve 431 shows the current through the coil inthe positive half of the converter for a phas (phase 1). A second curve432 shows the current through the coil in the negative half of theconverter for the same phase (phase 1). A third curve 433 shows thetotal amount of current of the AC source 703 for the same phase (phase1). A fourth curve 437 shows the total amount of current from thebattery 701 to the positive half of the converter for all three phases(phase 1, phase 2 and phase 3). A fifth curve 438 shows the total amountof current to the battery 702 from the negative half of the converterfor all three phases (phase 1, phase 2 and phase 3). To the first curve431, and the second curve 432, and the third curve 433, and the fourthcurve 437, as well as the fifth curve 438 it applies that a first periodof time 434 shows supply exclusively from the batteries 701, 102, and asecond period of time 435 shows a ramp-in course with supply from thebatteries 701, 702 and the AC source 703, where the current from thebatteries 701, 702 is reduced i pace with the current from the AC source703 being increased, and also a third period of time 436 that showssupply exclusively from the AC source 703.

[0045] The indication of functionality for the ramp-in course for athree-phase combined AC-DC to DC converter 700, 740, 780 with positiveas well as negative output voltage, in accordance with FIG. 4, followsthe indication of functionality for the ramp-in course for asingle-phase combined AC-DC to DC converter 100 with positive as well asnegative output voltage, in accordance with FIG. 2. It is noted that thebatteries 701, 702 are shared (and identical) for converters 700, 740,780 for all three phases (phase 1, phase 2 and phase 3). Batteries 701,702 delivers to three otherwise independent circuits 700, 740, 780 thateach corresponds to a single-phase combined AC-DC to DC converter 100with positive as well as negative output voltage, in accordance withFIG. 1. This means that the battery 701 is connected to three tyristorsin each their circuit 700, 740, 780, and the battery 702 is connected tothree tyristors in each of the same three circuits. The three circuits700, 740, 780 use each their phase, where the common point of reference704 is shared for the three phases.

[0046]FIG. 5 shows curves of an overload course for a single-phasecombined AC-DC to DC converter 100 with positive as well as negativeoutput voltage. A first curve 539 shows the current load in percentagesrelative to an allowable upper current threshold. A second curve 531shows the current through the coil 112. A third curve 532 shows thecurrent through the coil 113. A fourth curve 533 shows the total amountof current of the single-phase AC source 103. To the first curve 539,and the second curve 531, and the third curve 532, and the fourth curve533 it applies that a first and third period of time 536 show normaloperation with supply exclusively from the single-phase AC source 103,and a second period of time 540 shows an overload course with supplyfrom both the batteries 101, 102 and the single-phase AC source 103,where the current from the batteries 101, 102 are of such magnitude thatthe current from the single-phase AC source 103 is kept constant andalso within certain allowable current thresholds.

[0047] During the two periods 536 normal operations take place, wherethe single-phase AC source 103 alone delivers to the combined AC-DC toDC converter 100. During the period of time 540 an overload courseoccurs, where supply takes place from both the batteries 101, 102 andthe single-phase AC source 103. The pulse current from the batteries101, 102 is adjusted to such magnitude that compensation is fully madefor the overload, whereby the current from the single-phase AC source103 is kept constant and within certain allowable thresholds.

[0048]FIG. 6 shows curves of an overload course for a three-phasecombined AC-DC to DC converter 700, 740, 780 with positive as well asnegative output voltage. A first curve 639 shows the current load aspercentages on all three phases relative to an allowable upper currentthreshold. A second curve 631 shows the current through the coil in thepositive half of the converter for a phase (phase 1). A third curve 632shows the current through the coil in the negative half of the converterfor same phase (phase 1). A fourth curve 633 shows the total amount ofcurrent of the AC source 703 for the same phase (phase 1). A fifth curve637 shows the total amount of current from the battery 701 to thepositive half of the converter to all three phases (phase 1, phase 2 andphase 3). A sixth curve 638 shows the total amount of current to thebattery 702 from the negative half of the converter from all threephases (phase 1, phase 2 and phase 3). To the first curve 639, and thesecond curve 631, and the third curve 632, and the fourth curve 633 itapplies that a first and third period of time 636 show normal operationwith supply exclusively from the AC source 703, and a second period oftime 640 that shows an overload course with supply from both thebatteries 701, 702 and the AC source 703, where the current from thebatteries 701, 702 is of such magnitude that the current from the ACsource 703 is kept constant and further within given allowable currentthresholds.

[0049] The indication of functionality for the overload course for athree-phase combined AC-DC to DC converter 700, 740, 780 with positiveas well as negative output power, in accordance with FIG. 6, follows theindication of functionality for the overload course for a single-phasecombined AC-DC to DC converter 100 with positive as well as negativeoutput load, in accordance with FIG. 5. It is noted that the batteries701, 702 are shared (and identical) for converters 700, 740, 780 for allthree phases (phase 1, phase 2 and phase 3). Batteries 701, 702 deliverto three otherwise independent circuits 700, 740, 780, that eachcorresponds to a single-phase combined AC-DC to DC converter 100 withpositive as well as negative output voltage, in accordance with FIG. 1.This means that the battery 701 is connected to three tyristors in eachtheir circuit 700, 740, 780 and the battery 702 is connected to threetyristors in each of the same three circuits. The three circuits 700,740, 7809 use each their phase, wherein the common point of reference704 is shared for the three phases.

[0050]FIG. 7 shows a three-phase combined AC-DC to DC converter withpositive as well as negative output voltage constructed by means ofthree converters 700, 740, 80 with shared DC supply 701, 702. Thepositive terminal on a battery 701 is connected to the anode on atyristor in each of the three converters 700, 740, 780 corresponding tothe tyristor 106 in FIG. 1. The negative terminal on the battery 701 isconnected to a common point of reference 704. The negative terminal on abattery 702 is connected to the cathode on a tyristor in each of thethree converters 700, 740, 780, corr sponding to the tyristor 107 inFIG. 1. The positive terminal on the battery 702 is connected to thecommon point of reference 704. A switch in each of the three converters700, 740, 780, corresponding to the switch 127 in FIG. 1, is connectedto each their phase on an AC source 703. The AC source 703 is furtherconnected to a common point of reference 704. The positive outputs ofthe three converters 700, 740, 780 are all connected to an output 725.The negative outputs of the three converters 700, 740, 780 are allconnected to an output 726. The references of the three converters 700,740, 780 are all connected to the point of reference 704.

[0051] The indication of functionality for a three-phase combined AC-DCto DC converter with positive as well as negative output voltageconstructed from three converters 700, 740, 780 with shared DC supply701, 702, in accordance with FIG. 7, follows the indication offunctionality for a single-phase combined AC-DC to DC converter 100 withpositive as well as negative output voltage, in accordance with FIG. 1.

[0052]FIG. 8 shows a three-phase combined AC-DC to DC converter withpositive output voltage constructed from three converters 800, 840, 880with shared DC supply 801. The positive terminal on a battery 801 isconnected to the anode on a tyristor in each of the three converters800, 840, 880, corresponding to the tyristor 306 in FIG. 3. The negativeterminal on the battery 801 is connected to a common point of reference804. A switch in each of the tree converters 800, 840, 880,corresponding to the switch 327 in FIG. 3, is connected to each theirphase on an AC source 803. The AC source 803 is further connected to acommon point of reference 804. The negative outputs of the threeconverters 800, 840, 880 are all connected to an output 825. Thereferences of the three converters 800, 840, 880 are all connected tothe point of reference 804.

[0053] The indication of functionality for a three-phase combined AC-DCto DC converter with positive as well as negative output voltageconstructed from three converters 800, 840, 880 with common DC supply801, in accordance with

[0054]FIG. 8, follows the indication of functionality for the positivehalf of a single-phase combined AC-DC to DC converter 100 with positiveas well as negative output voltage, in accordance with FIG. 1.

[0055] The converter (100, 300, 700, 740, 780, 800, 840, 880) can becharacterised eg in that—at a given load, typically full load—on atleast one DC output (125, 126, 325, 725, 726, 825) switches occuradaptively from a DC supply source (101, 102, 301, 701, 702, 801) to anAC supply source (103, 303, 703, 803), typically a diesel generator,while taking into consideration stability of frequency and voltage onthe AC supply source (103, 303, 703, 803). By such adaptive switch ofsource, gradual switching from the DC supply source to the AC supplysource will occur, where supply from both supply sources takes placeduring the switching time. The adaptive switch of source optionallycomprises that there are several, consecutive periods with supply fromboth supply sources. Finally, the adaptive switching of source meansthat it is possible to switch completely or partially back to the DCsupply source. Hereby a gentler coupling onto the AC supply source isobtained, where the converter does not expose the AC supply source toabrupt and forceful loading couplings. Hereby the AC source is protectedagainst overload with ensuing fluctuation of eg frequency and voltage.If the AC source is eg a diesel generator, it is important to avoidabrupt and forceful loading couplings, since they translate onto therotor current, whereby the diesel generator becomes instable with regardto both frequency and voltage. In a worst-case scenario, the instabilitymay result in self-oscillation with ensuing supply failures.

[0056] The converter (100, 300, 700, 740, 780, 800, 840, 880) can be egcharacterised in that—upon supply from an AC supply source (103, 303,703, 803), typically a diesel generator, dynamic load changes arecompensated, where the current from at least one DC output (125, 126,325, 725, 726, 825) is increased adaptively. The adaptive compensationof dynamic load changes occurs with due regard to stability of frequencyand voltage on the AC supply source (103, 303, 703, 803) by obtainingsupplementary energy from a DC supply source (101, 102, 301, 701, 702,801). By such adaptive compensation of dynamic load changes, asupplementary supply from the DC supply source will occur, in thatsupply will—for a period of time—take place from both supply sources.Optionally there may be several consecutive periods with supply fromboth supply sources. Hereby a gentler load onto the AC supply source isobtained, where the converter does not expose the AC supply source toabrupt and forceful loading couplings. Hereby the AC source is protectedagainst overload with ensuing fluctuation of eg frequency and voltage.If the AC source is eg a diesel generator, it is important to avoidabrupt and forceful loading couplings, since they translate onto therotor current. Hereby the diesel generator becomes instable with regardto both frequency and voltage, and in a worst-case scenario, theinstability may result in self-oscillation with ensuing supply failures.

1. A converter (300) for providing at least one DC output (325) from atleast one AC supply (303) with at least one phase and at least one DCsupply (301), said AC supply supplying an AC signal comprising positiveand negative half-periods, the converter comprises at least one coil(312) that is in connection with said at least one DC output, theconverter contains controllable contact means (327) adapted forconnecting and disconnecting said AC supply and said DC supply to/fromsaid converter characterised in that connecting and disconnecting ofsupply sources to/from said converter is based on phase information ofthe AC signal (233), whereby the supply signal fed to said coil(231;232) is divided into periods, wherein the periods of the supplysignal alternatingly originate from either positive or negativehalf-periods of the AC signal (233) and current pulses from said DCsupply; and wherein the current pulses from the DC supply are regulatedin dependence of the AC signal; and wherein the converter contains meansfor voltage regulating said at least one DC output.
 2. A converter (300)according to claim 1, characterised in that the AC supply source (303)is a single-phase AC source.
 3. A converter (700, 740, 780, 800, 840,880) according to claim 1, characterised in that the AC supply source(703, 803) is a poly-phase AC source.
 4. A converter (100, 300, 700,740, 780, 800, 840, 880) according to at least one of claims 1 through3, characterised in that—on the basis of a signal from a currentdetector (114, 115, 314) that measures the current through a coil (112,113, 312), a control circuit (108, 109, 308) has means for connectingand disconnecting, respectively, the second terminal of the coil (112,113, 312) to a DC supply source (101, 102, 301, 701, 702, 801), andmeans for connecting and disconnecting, respectively, the secondterminal of the coil (112, 113, 312) to a common point of reference(104, 304, 704, 804); and that the current through the coil (112, 113,312) flows to the DC output (125, 126, 325, 725, 726, 825) of theconverter (100, 300, 700, 740, 780, 800, 840, 880) during periods oftime, where the second terminal of the coil (112, 113, 312) is notconnected to the common point of reference (104, 304, 704, 804); andthat the converter (100, 300, 700, 740, 780, 800, 840, 880) has meansfor connecting and disconnecting, respectively, an AC supply source(103, 303, 703, 803) to/from the one terminal of the coil (112, 113,312).
 5. A converter (100, 700, 740, 780) according to at least one ofclaims 1 through 4, characterised in that at least one converter (300)is used to form a positive DC output (125, 725) relative to a commonpoint of reference (104, 704); and at least one converter is used toform a negative DC output (126, 726) relative to a common point ofreference (104, 704).
 6. A converter (100, 700, 740, 780) according toclaim 5, characterised in that the AC supply source (103, 703) is sharedby converters (300) that are used to form a positive output voltage andconverters that are used to form a negative output voltage,respectively, relative to a common point of reference (104,704).
 7. Aconverter (100, 300, 700, 740, 780, 800, 840, 880) according to at leastone of claims 4 through 6, characterised in that the means forconnecting and disconnecting, respectively, the one terminal of the coil(112, 113, 312) to/from a DC supply source (101, 102, 301, 701, 702,801) is a controllable switch (106, 107, 306); and that the controllableswitch (106, 107, 306) can be regulated to be connected for at least apart of every other half-period.
 8. A converter (100, 300, 700, 740,780, 800, 840, 880) according to at least one of claims 4 through 7,characterised in that the means for connecting and disconnecting,respectively, the second terminal of the coil (112, 113, 312) to/from acommon point of reference (104, 304, 704, 804) is a controllable switch(110, 111, 310); and that the controllable switch (110; 111; 310) can beregulated to be connected for at least a part of every otherhalf-period; and that the controllable switch (110; 111; 310) istypically connected in burst series.
 9. A converter (100, 300, 700, 740,780, 800, 840, 880) according to at least one of claims 4 through 8,characterised in that semi-conductors are used as controllable switches(106, 107, 110, 111, 306, 310) comprising at least one of the typesfield power transistor, bipolar transistor, Insulated Gate BipolarTransistor (IGBT), Gate Turn-Off Tyristor (GTO) and Injection EnhancedGate Transistor (IEGT).
 10. A converter (100, 300, 700, 740, 780, 800,840, 880) according to at least one of claims 1 through 9, characterisedin that, in an overload situation, the current from the AC supply source(103, 303, 703, 803) is limited to a constant maximum value, in thatsupplementary energy is supplied by the DC supply source (101, 102, 301,701, 702, 801).